John III (Swedish: Johan III; 20 December 1537 – 17 November 1592) was King of Sweden from 1569 until his death. He attained the Swedish throne after a rebellion against his half-brother Erik XIV. He is mainly remembered for his attempts to close the gap between the newly established Lutheran Church of Sweden and the Catholic Church, as well as his conflict with and possible murder of his brother.
John was also, quite autonomously, the Duke of Finland from 1556 to 1563. In 1581 he assumed the title Grand Duke of Finland. His first wife was Catherine Jagiellon of the Polish–Lithuanian ruling family, and their son Sigismund eventually ascended both the Polish–Lithuanian and Swedish thrones. He ended the Northern Seven Years' War, but instead Sweden was drawn into the 25 Years' War with Russia, where minor gains were eventually made. He worked for closer relations with Poland. John III was interested in religion and culture. During his reign, he countered the growing Lutheran tendencies of the Church of Sweden under the influence of Duke Charles, and worked for a reunion with the Catholic Church and the Pope in Rome.